Aquarius WD440 - Washer/Dryer - Dryer not heating up?

HELP! I have a Hotpoint Aquarius WD440. The wash cycle seems to be fine. However, when I set it to dry, it does the usual cycle for drying but doesn't actually heat up, so the clothes are still wet when I take them out. I've checked the manual and it doesn't seem to be any of the problems that the manual suggests it might be. Thanks.